Adsorption and reaction of water on oxidized tungsten: thermal desorption and electron stimulated desorption measurements

Abstract

The adsorption and decomposition of water, H 2 18O, on an 16O-oxidized W(100) surface have been examined over a wide temperature range (25–700 K) with thermal desorption spectroscopy (TDS), low energy ion scattering (LEIS) and electron stimulated desorption (ESD), and ESD ion angular distribution (ESDIAD). TDS is used to determine the coverage and the range of desorption temperature of H 2 18O, and to identify desorption products from the oxidized W(100) surface, while ESD and ESDIAD are used to monitor the surface chemistry of H 2 18O on the oxidized W(100) surface. ESD and ESDIAD data show no evidence for diffusion of H 2 18O on the oxidized W(100) surface between 25 K and 120 K. TDS demonstrates that the majority of water adsorbed in the first monolayer at 25 K remains molecular and desorbs with a peak temperature of ∼ 155 K. However, both TDS and ESD measurements indicate that a very small percentage of H 2 18O (∼8% of a monolayer) dissociates upon adsorption at 25 K to form adsorbed 16OH and 18OH. No stable OH species remains on the oxidized W(100) surface above about 350 K.